1. Field of the Invention
This invention is directed toward the operation of instrumentation within a well borehole, and more particularly directed toward formation logging, perforating, casing inspection, and other operations in borehole that deviate significantly from vertical, wherein required borehole instrumentation is conveyed by a continuous sucker rod and injector system.
2. Description of the Related Art
Modern oil and gas wells are typically drilled with a rotary drill bit and a circulating drilling fluid or “mud” system. The mud system (a) serves as a means for removing drill bit cuttings from the well as the borehole is advanced, (b) lubricates and cools the rotating drill bit, and (c) provides pressure within the borehole to balance internal pressures of formations penetrated by the borehole. Rotary motion is imparted to the drill bit by rotation of a drill string to which the bit is attached. Alternately, the bit is rotated by a mud motor which is attached to the drill string just above the drill bit. The mud motor is powered by the circulating mud system. Subsequent to the drilling of a well, or alternately at intermediate periods during the drilling process, the borehole is cased typically with steel casing, and the annulus between the borehole and the outer surface of the casing is filled with cement. The casing preserves the integrity of the borehole by preventing collapse or cave-in. The cement annulus hydraulically isolates formation zones penetrated by the borehole that are at different internal formation pressures.
Numerous operations occur in the well borehole after casing is “set”. All operations require the insertion of some type of instrumentation or hardware within the borehole. Examples of typical borehole operations include:                (a) wireline logging to determine various formation parameters including hydrocarbon saturation;        (b) perforating of the casing in prospective zones so that hydrocarbons can be produced;        (c) setting packers and plugs to isolate producing zones;        (d) inserting tubing within the casing and extending the tubing to the prospective producing zone;        (e) logging with instruments conveyed with coiled tubing; and        (f) installing artificial lift equipment for producing zones with insufficient pressure to flow to the surface of the earth.Some borehole operations are typically performed during the drilling of the well, such as logging while the well is being drilled using instrumentation conveyed by the drill string, intermediate wireline logging, directional surveying of the well, and directional steering of the drill bit during the drilling operation. Other borehole operations are performed during the life of the well and at the end of the life of the well, such as logging, casing inspection, perforation plugging, and resetting of packers and plugs.        
Early oil and gas wells were typically drilled in a vertical or near vertical direction with respect to the surface of the earth. As drilling technology improved and as economic and environmental demands required, an increasing number of wells were drilled at angles which deviated significantly from vertical. As an example, fifty or more wells are commonly drilled in a variety of directions from a single offshore platform. In the 1990's, drilling horizontally within producing zones became popular as a means of increasing production by increasing the effective borehole wall surface exposed to the producing formation. It was not uncommon to drill sections of boreholes horizontally (i.e. parallel to the surface of the earth) or even “up-hill” where sections of the borehole were actually drilled toward the surface of the earth.
The advent of severely deviated boreholes introduced numerous problems in the performance of borehole operations. Conventional wireline logging was especially impacted. Wireline logging utilizes the force or gravity to convey logging instrumentation into a borehole. Gravity is not a suitable conveyance force in highly deviated, horizontal or up-hill sections of boreholes. Numerous methods have been used, with only limited success, to convey conventional wireline instrumentation or “tools” in highly deviated conditions. These methods include conveyance using a drill string, a coiled tubing, and a hydraulic tractor. All methods require extensive well site equipment, and often present severe operational, economic, and logistic problems. In general, conveyance of conventional wireline tools by means other than gravity are, at best, marginally successful.
An entire field of formation evaluation has been developed around the basic concept of measuring formation parameters while the borehole is being drilled. This methodology requires specially designed measurement-while-drilling (MWD) or logging-while-drilling (LWD) instrumentation. The instrumentation is conveyed by the drill string, and is mounted in the drill string near the drill bit. MWD and LWD systems are effective in highly deviated boreholes, and modern systems rival their wireline counterparts in accuracy and precision. The techniques do, however, require the use of a drilling or service rig that is generally expensive and often operationally impractical in older and more remote wells. In addition, any tubing in the well must be pulled, thereby adding to the monetary and operational expense. It should also be noted that drill strings have been used as a means of conveyance and operation of other types of equipment such as packers and plugs, but also at great operational and monetary expense.
Conventional wireline and other well service systems have been configured for coiled tubing conveyance. This method of conveyance is operable in highly deviated well boreholes. Although not as costly as drill string conveyed equipment requiring a drilling or service rig, coiled tubing and associated injector equipment is still physically large and presents many drawbacks that are encountered with drill string conveyed systems.
Downhole tractors are designed to literally pull downhole instrumentation and hardware in highly deviated boreholes. Tractors utilize rotating radial members which grip the walls of the borehole and therefore convey the tractor axially along the borehole. Tractors are relatively complicated, hydraulically operated pieces of equipment and lack reliability, especially in deep wells and wells with highly corrosive borehole fluids.
In view of the above discussion, it is apparent that a reliable, relatively inexpensive, versatile and operationally efficient system is needed to convey and operate borehole equipment in boreholes which are highly deviated from the vertical.